1. Field of the Invention
The present invention relates to a plasma reactor used in a semiconductor fabrication process. More particularly, the present invention relates to an Inductive Coupled Plasma (ICP) type plasma reactor and an etching method using the same.
2. Description of the Related Art
In recent years, as a Critical Dimension (CD) of a workpiece pattern obtained from etching is reduced to 50 nm or less in an etching process of a plasma reactor, a thickness of a photoresist layer used as an etch mask of a workpiece gets thinner. This makes it very difficult for a very thin photoresist pattern to sufficiently protect a region of a workpiece not to etch from plasma in the etching process for obtaining a pattern of a high aspect ratio (i.e., a pattern of a large H/W ratio (H: Height of workpiece pattern obtained from etching and W: Width of workpiece pattern obtained from etching)). To solve this problem, used is a multi-stack structure etch mask having a hard mask layer inserted between the photoresist pattern and the workpiece.
Compared to the etching process carried out with only the photoresist pattern laminated on the workpiece, an etching process using the multi-stack structure etch mask is much more complex. For example, a case that the hard mask layer is an Amorphous Carbon Layer (ACL) and Bottom Anti-Reflection Coating (BARC) film, and the workpiece to be etched is an oxide film can be taken into consideration. In this case, etching the ACL or BARC film requires a chemical etching process by high density plasma including a large amount of reactive ions and radical particles. On the other hand, etching the oxide film having a strong bonding structure requires a physical etching process by low density plasma having high ion energy. In case that the oxide film is etched by the low density plasma having the high ion energy, a relatively high selectivity (i.e., a ratio of Etch Rate (ER) of hard mask layer to ER of oxide film) can be maintained.
In case that the multi-stack structure etch mask is used for etching the oxide film as above, an etching condition of the hard mask layer is different from an etching condition of the oxide film. Because of this, there is a need to change a plasma density within a reaction chamber in course of the etching process to continuously etch the hard mask layer and the oxide film by one plasma reactor. However, the conventional plasma reactor is difficult to freely change the plasma density in course of the etching process. Accordingly, there is a need for two plasma reactors each set to the etching conditions to etch the hard mask layer and the oxide film.
On the other hand, as a workpiece (e.g., a wafer or glass substrate) becomes larger to a diameter of 300 nm or more, there occurs a phenomenon in which ERs of a center part and edge part of the workpiece are given different from each other, or a CD of a pattern formed in the center part of the workpiece after the etching process and a CD of a pattern formed in the edge part are given different from each other. This phenomenon frequently occurs when a concentration of a reactive gas of the center part of the workpiece within the reactive chamber is different from a concentration of a reactive gas of the edge part or when a density of a pattern to be formed in the center part of the workpiece is different from a density of a pattern to be formed in the edge part of the workpiece. Also, due to the phenomenon in which the ERs of the center part and edge part of the workpiece are given differently from each other, it is very difficult to secure process uniformity when etching the workpiece having the multi-stack structure etch mask laminated thereon. That is, it is difficult to secure the uniform ER in the center part and edge part of the large workpiece.